Anything you can afford and afford to feed. Practice is very important. Surplus bolt action rifles can be gotten for as little as $100 and there is still surplus ammo available reasonably cheap.
If you have the money and don’t live in a communist state, a semi-auto in 5.56x45, 7.62x39 or 7.62x51.
Ruger mini 30, AK variant or an AR variant. Ruger has a very nice AR556 that I’ve seen as low as $535
Much obliged. Christmas is coming up and wifey asked what I want. :-)